The present invention relates to fluorescent lamps and more particularly to a fluorescent lamp adapted for illuminating food in grocery stores, meat markets, and other places where food, particularly meat, is displayed.
There is currently a market for specialty fluorescent lamps for use in grocery stores, meat markets, other shops where food is displayed, etc. The lamps satisfying this market have reduced ultraviolet emission and typically have a large amount of radiation in the red region of the spectrum. The latter is provided by phosphors, such as magnesium fluorogermanate activated with manganese emitting in a narrow band near 650 nm and/or yttrium oxide activated with europium emitting in a narrow band at 611 nm. These phosphors have the disadvantage of being expensive. Further, while enhancing red colors, these lamps otherwise do not provide natural color rendition as measured by the CIE color rendition index.
There is a need for a fluorescent lamp which renders the color of foods more vivid and appealing than under typical halophosphate and tri-color lamps and which does so without giving an unnatural color appearance or a preponderance of red color.
There is also a need for a fluorescent lamp which achieves the desired customer color effects on foods without using rare or expensive phosphors. The two preferred phosphors used in the present invention, (Sr,Mg,Ca)3(PO4)2:Sn2+ (note that Mg and/or Ca can be zero) and Ca5(PO4)3F:Sb3+, are both common and less costly.
A mercury vapor discharge lamp comprising a glass envelope, means for providing a discharge, a discharge-sustaining fill of mercury and an inert gas sealed inside said envelope, and a phosphor-containing layer coated inside said glass envelope, said phosphor-containing layer containing not more than two phosphors, said phosphor-containing layer containing a blend of a first phosphor and a second phosphor, said first phosphor having an emission band with a maximum between 610 and 645 nm and having a width at half maximum of at least 50 nm, said second phosphor having an emission band with a maximum between 465 and 495 nm and having a width at half maximum of at least 50 nm.